Terrible Mileage with 7.3 IDI w/ turbo - WHY? - Ford Powerstroke Diesel Forum
7.3L IDI (Non-Powerstroke) Diesels Technical discussion of topics related to vehicles powered by the 7.3 Liter In-Direct Injection Navistar engines.

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post #1 of 17 Old 06-15-2009, 09:29 AM Thread Starter
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Terrible Mileage with 7.3 IDI w/ turbo - WHY?

I have a 1992 F350 crew cab long box with the 7.3 IDI and an aftermarket ATS turbo. It appears everything else is stock. I am getting about 11 mpg while driving around. And about 10mpg while towing my 25' gooseneck.

Everywhere else I read on this forum points that I should get much better while driving around not towing.

The truck has 177k and the towing gears I cannot remember what I read underneath. 4. something. It is a 4x4 but its not engaged. I just had coolant flushed, oil changed, and gear oils changed and still no increase in mileage. I even tried adding the Lucas fuel additives with no luck there either.

any ideas?

thanks,
Dozer
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post #2 of 17 Old 06-15-2009, 09:43 AM
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I dunno much about those years, but you gotta remember that it's a 444CI motor without the fancy injection system that powerstrokes have. If you think of it along the lines of an old 460, then you're completely normal at 10mpg's with a trailer. My 97 w/460 was lucky to get 10 with just a two horse trailer.
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post #3 of 17 Old 06-15-2009, 09:48 AM
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i get about 10 in my 99. you have a big motor. it likes fuel


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post #4 of 17 Old 06-15-2009, 09:50 AM
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Just called a buddy of mine with an 86? 6.9 that has the ATS turbo kit on it. He says his best ever was 13MPG. Usually around 11, and his is a bit little smaller than yours. If you figure out any tricks for these dinosaurs, post it up so I can pass it on.
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post #5 of 17 Old 06-15-2009, 01:11 PM Thread Starter
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Well I looked around these forums for awhile and seen claims from IDI engines of 17-18 and up to 22 if driven nicely. I know that everything on the internet needs to be taken with a grain of salt but I didn't expect to be that bad. My last diesel ( a 99 F350 w/ 7.3PSD) Honestly averaged 17 between country roads and highways. I expected this one to be similiar.

I am not concerned about the towing part since I figured that would be poor. What I didn't expect was unhooking it didn't change my mileage.
thanks
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post #6 of 17 Old 06-15-2009, 07:33 PM
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From my experience with my 1990 4x4 7.3 diesel reg cab 8ft bed your mileage is on the low side. First of all with the turbo your pump is turned up a which hurts mileage a bit. The next big factor is tires. Depending on what kind you have it will make a big difference in mileage. When I got my truck last fall I had passenger tires on it. I drove from Chicago to Milwaukee hauling 1000lbs in the bed and got 18mpg with the cruise set at 60. I got some larger 265 75 15's with a load range of E which is one hell of a heavy but strong tire and now I can only get 14-15 no matter what I do. The rolling mass is just so much more compared to the old wimpy tires and it hurt my mileage.

The other factor that most people overlook is injectors. Most folks think that as long as a truck is running the injectors are good. Injectors usually go 100k or so and they need to be replaced for OPTIMUM performance and fuel economy. Yes they will last and work for much much longer but not as efficiently when it comes to fuel economy. As fuel goes up they pay for themselves fast if you drive alot. I was lucky enough to have mine already done. Injectors are a wear item that should be replaced to keep optimum fuel economy and power. I put injectors in a lot of diesels primary older diesel Mercedes but in GM's and Fords and it makes a difference, the car or truck will just run better overall. If you have 177k on original injectors I would bet that they are definitely hurting mileage. Hope this will help
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post #7 of 17 Old 06-15-2009, 09:16 PM
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Between my Dad and I we have had 2 6.9's, and 3 7.3 IDI's and the 6.9's killed the 7.3's in the milage category for sure. Out of the five only the '94 7.3 has a turbo and it does not get great milage with out the hydrogen kit I have on it. I have found that when the pump is tuned right (up) the milage goes up since you don't have to push it as hard to maintain speed. We turned the pump up on every IDI we have and the milage jumped 2-3 mpg, if you keep your foot in them they will use more. My '94 (with 306,000 miles)can obtain over 20mpg with hydrogen and about 14 mpg without it. The 6.9's were both able to get over 20mpg on fuel only( one of these trucks has over 500,000 miles on it at this time). The IDI's are great motors when tuned right with great low-end power! Hydrogen is the best thing I have done for my IDI's, most people are skeptical, but it works for me.
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post #8 of 17 Old 06-16-2009, 06:10 AM
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I put a 7.3 turbo in my '76 crew cab for just that reason. With the 390fe motor it was getting 9-11mpg, now I get 16+. 11mpg is a little low, depending on your gearing, tires, driving style, ect. you should be getting at least 14. Mine is a high boy 4x4 with over sized tires and I don't drive too nice either. Also, the injector pumps in these trucks are usually only good for 100-150k, same story as the injectors, the truck might seem to run ok, but....
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post #9 of 17 Old 06-16-2009, 07:43 AM Thread Starter
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I like to think I drive quite calmly. I have stock tires. I will have my mechanic look at the shape of the injectors and the shape of the turbo to make sure its not going out.

What is the deal with hydrogen? If I can make a kit what is all needed and if I need to buy one who makes a kit for a 7.3 IDI? I am starting to seriously look at this as an option but I have yet to find anything that explains how it works while towing vs. freewheeling.

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post #10 of 17 Old 06-16-2009, 09:25 AM
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x2 on the hydrogen.. heard good and bad.
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